The present invention relates generally to long tape measures and more particularly to the composition of the measuring tapes used in long tape measures.
Measuring tapes are originally thought of as embodying a symmetrical configuration defined by two parallel faces disposed on opposite sides of a central plane. One of the faces contains measurement markings printed thereon.
There have been many efforts to enhance the measuring effectiveness of measuring tapes by altering their composition so as to reduce tape elongation, or stretching while maintaining tape flexibility. Stretching in measuring tapes leads to erroneous measurements and reduces the accuracy of the tape.
Examples of measuring tapes including composition of inorganic fibers, organic fibers or a combination thereof incorporated within a coating are disclosed in the following patents: U.S. Pat. Nos. 2,321,920, 4,459,753 and 5,095,632; and United Kingdom Patent Application No. 2 123 955 A.
The ""920 patent teaches a measuring tape having a woven fabric strip of inorganic material such as glass fibers combined with organic material such as cotton or linen fibers and coated with an impregnating coating. The ""955 application is similar in that glass yarn is used to form a longitudinal reinforcement layer and gives dimensional stability to the tape. The ""955 application further teaches incorporating glass fibers surrounded by layers of natural or artificial fibers within a polyvinyl chloride (PVC) matrix. Both of these efforts result in a measuring tape that is adequately flexible, however, both lengthen when subjected to stresses during normal operation. Lengthening of the tape leads to erroneous measurements.
The ""753 patent is similar to the ""920 patent, in that it teaches the use of woven glass fibers are impregnated with thermosetting resin. The ""753 patent differs in that it also teaches the use of carbon fibers in the woven structure instead of glass fibers. The ""632 patent teaches a structure formed of a plurality of aligned, overlapped, relatively thin and narrow strips of carbon fibers impregnated with thermoplastic resin (polyphenylene sulfide) to have a low coefficient of thermal expansion along the length axis, i.e. it has a very low distortion with respect to thermal expansion.
Applicant has found that the formation of measuring tapes from a glass fiber structure impregnated with resin or a carbon fiber structure impregnated with resin do not achieve desired tape elongation stability characteristics. Moreover, in some applications, measuring tapes are used around work areas containing sharp objects, such as construction sites. Usage in these areas makes it desirable to reduce the blade""s ability to be cut by being pulled over a sharp comer or run over by a sharp object. Applicant has also found that such sharp objects frequently cut the measuring tapes formed from a glass fiber structure impregnated with resin or a carbon fiber structure impregnated with resin.
Generally, metal measuring tapes provide a durable construction with a high resistance to being cut by sharp objects. Metal measuring tapes are made from steel, which has a high elastic modulus and exhibits great toughness. Increased modulus corresponds to a proportional decrease in tape elongation and results in more accurate measurements. In addition, steel has a greater toughness than carbon and fiberglass and this difference in mechanical properties allows steel to be significantly more cut resistant than either carbon or fiberglass. However, steel is not a flexible material and tends to keep its shape when kinked. The kinking of the steel reduces the measurement accuracy of the tape, even after the kinks are straightened.
Consequently, there exists a need in the art for a measuring tape that has the advantages of balancing stretch resistance, cut resistance and cost.
It is an object of the present invention to provide a measuring tape that meets the needs described above. In accordance with the principles of the present invention, this objective is accomplished by providing a measuring tape comprising an elongated blade of a plastic material reinforced by a transverse array of longitudinally extending continuous filaments. The array of continuous filaments includes grouped carbon filaments of a volume constituting 0 to 90% of the total volume of filaments, steel filaments of a volume constituting 0 to 90% of the total volume of filaments and fiberglass filaments grouped in strands of a volume constituting 0 to 90% of the total volume of filaments.
An object of the present invention is also achieved by providing a long tape comprising a casing and a reel member being rotatably mounted within the casing for relative movement thereto. An actuating member accessible on an exterior of the casing for manually moving the reel member relative to the casing and extending through the casing to be received within the reel member rotatably mounted within the casing. A measuring tape is wound around the reel member and has one end thereof extending from the casing configured and arranged to be retractable towards the casing by the actuating member. The measuring tape comprises an elongated blade of a plastic material reinforced by a transverse array of longitudinally extending continuous filaments. The array of continuous filaments includes grouped carbon filaments of a volume constituting 0 to 90% of the total volume of filaments, steel filaments of a volume constituting 0 to 90% of the total volume of filaments and fiberglass filaments grouped in strands of a volume constituting 0 to 90% of the total volume of filaments.
Other objects, features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.